Information stored in a disk drive can be stored in binary form as either a logical one (1) or a logical zero (0), with the information being encoded as a magnetic flux on a magnetic platter of the disk drive. Typically, a logical one is represented as a transition in a magnetic flux on the magnetic platter while a logical zero is represented as an absence of a transition in a magnetic flux. The magnetic flux on the magnetic platter can be affected by an inductive write head. The transitions in the magnetic flux can be created by switching the polarity of a write current on the inductive write head. Since it takes a finite amount of time to change the polarity of a write current applied by the inductive write head, the transitions in the magnetic flux can consume a finite amount of space on the magnetic platter. A fast magnetic flux transition will require a small amount of space, while a slow magnetic flux transition will require a large amount of space. Since the amount of space on a magnetic platter is fixed, a faster rate of transition in the magnetic flux can mean that more information can be stored in the disk drive.
With reference now to FIG. 1, there is shown a diagram illustrating a portion of an exemplary disk drive 100. The disk drive 100 includes a magnetic platter 105, however, some disk drives may have more than one magnetic platter. The magnetic platter 105 is used to store the information written by an inductive write head 110. The information is stored on the magnetic platter 105 in the form of magnetic flux and transitions in the magnetic flux. A writer circuit 115 is used to provide a write current to the inductive write head 110. A steady state write current flowing through the inductive write head 110 will produce a magnetic flux of a certain magnitude. A transition in the magnetic flux can be achieved by switching a polarity of the write current flowing through the inductive write head 110.
Output capacitances associated with writer circuit 115 combined with the inductive nature of the inductive write head 110 can cause ringing in the write current, which can delay the settling of the write current to a steady state DC value after the occurrence of a switch in the polarity of the write current. The ringing can negatively affect the placement of the transition on the magnetic platter as well as the size of the transition. The placement of the transition can negatively affect the reliability of the disk drive 100, while the size of the transition affects the amount of information that can be stored in the disk drive 100.
A prior art technique that has been used to reduce the ringing in the write current after a polarity switch is to use matching resistors on the inductive write heads. The matching resistors can reduce an impedance mismatch between the write circuitry and the inductive write head, thereby reducing the ringing in the write current.
Another prior art technique that has been used to reduce the ringing in the write current is to switch the polarity of the write current prior to the write current reaching a steady state value. This can remove the need to wait for the write current to settle, effectively shortening the duration of the ringing, and therefore maintains a fast transition write current, enabling increased storage capacity in the disk drive.
One disadvantage of the prior art is that the matching resistors can dissipate a portion of the write current being provided to the inductive write head. The reduced write current can negatively affect the transition time of the write current, therefore, extending the transition of the magnetic flux and decreasing the storage capacity of the disk drive.
Another disadvantage of the prior art is that the switching of the polarity of the write current prior to the write current reaching a steady state can decrease placement accuracy of the information being written to the magnetic platter and can result in a decrease in the reliability of the disk drive. Furthermore, if the switching of the write current occurs while the write current has not fully settled from a prior transition, the switching of the write current may result in unexpected and undesired current levels.